These reforms are all a part of the general 'westernization' of Selim III with the game reflecting this in a military reform and an economic reform. So you will want to do both; however, understand that the conservative side of Ottoman society will likely oppose the reforms in future years which you may need to address with future counter reform options. But as the reforms bring European style corps and such to replace the Janissary formations, you definitely want to reform

I have digged a bit in the event code. Have I understood correctly, that a chance of 25% exists over a rather long period of time to backfire. Is that correct and if so, has anybody ever successfully reformed Ottos?